WATERSHED ANALYSIS OF THE EBERSWALDE DELTA (EARLY HESPERIAN), MARS

The Eberswalde Delta is an impressive Martian delta fed by an Earth-like dendritic fluvial system. This study is designed to quantify controls on its network morphometry and maturity using ArcGIS Pro, MRO Context Camera images (6 m/pixel), and DEMs (20 m). Long profiles, upstream contributing area (km²), channel depth (m), width (m), width/depth (W/D), and slope (m/m) were calculated. Channel degradation is accounted for using estimates for age (~3.5 Ga) and estimated global degradation rates.

The watershed is west of Eberswalde crater and north of Holden crater; it incises into the continuous ejecta of Holden, which post-dates Eberswalde. Water was sourced from west to east over elevated Holden ejecta, emptying into Eberswalde. Yet, upland channels first converge into a sub-basin west of Eberswalde’s rim before spilling over into the crater through a breach. Long profiles reflect this path and contain two convex-up knickzones where the channels enter (1) the sub-basin and (2) Eberswalde crater. W/D ranged from 40 within steeper upland canyons and along the rim of Eberswalde, to 100 in the sub-basin. Slope on a 10-km scale varies between 0.01 and 0.04 m/m in the headwaters and the main trunk channel, and between 0 and 0.01 m/m in the sub-basin.

After adjusting for degradation, all streams were at least tens of meters deep. Yet, many of the first-order channels headward eroded to drainage divides, reflected by a near-zero upstream contributing area. Thus, the network may have been volumetrically larger but not much more complex when it formed. The lower order, upland streams have similar geomorphic characteristics to the main trunk channel that feeds Eberswalde, in terms of convex-up dis-equilibrium long profiles, W/D ratios, and slopes. The convex-up knickzones in both the upland reach and main trunk channel suggest that the channels failed to reach equilibrium, attesting to the immaturity of the system.

The enclosed topography of the sub-basin, presence of an elevated breach at its eastern edge, and observations of light-toned layered materials on its floor suggest that the sub-basin held a transient lake that was separate from the putative lake in Eberswalde crater. Incised meanders and knickpoints are present in both reaches, suggesting variation in local base level during formation, possibly controlled by water level.